1. Field of the Invention
This invention relates generally to the detection of a temperature range or a temperature of a wheel or bearing of a railway vehicle. More specifically, the invention relates to collecting an infrared (IR) radiation wavelength spectrum radiating from the wheel or bearing of a train traversing a railroad track that is indicative of the temperature range or the temperature of the wheel or bearing.
2. Brief Description of the Prior Art
In order to protect against railroad car wheel or bearing failures, most railroads utilize heat detectors along their rights of way and in close proximity to their railroad tracks. Such detectors view, through infrared scanners, the bearing and wheel of a passing train. If an overheated wheel or bearing is detected, an alarm is triggered to alert the train operator that an overheated wheel or bearing has been detected.
The infrared scanner and associated circuits for detecting an overheated wheel or bearing are available commercially. Some systems utilize an infrared detector located in close proximity to a railroad track such that the detectors detects the presence of a hot wheel or bearing traversing the railway line. For example, a thermal detector is responsive to IR energy in the wavelength range of 6 to 14 microns. Such systems commonly use a lens and filter to collect the radiated infrared waves from the wheel or bearing and focus the collected infrared radiation within the predefined wavelength range directly onto an infrared detection device. The infrared detection device is only provided the range of wavelengths of infrared spectrum that is passed through the filter. The filter wavelength range is chosen to specify wavelengths that represent a hot wheel or hot bearing condition. The infrared detection device determines the presence of the wavelengths within the filtered wavelength range and produces an output signal indicative of the power or intensity of such infrared radiation within the predefined bandwidth range. In such prior art systems, an increase in the magnitude of the radiation within the wavelength range results in an increase in the voltage or current generated by the detector.
One such infrared detection device is a pyroelectric cell equipped with a lithium tantalate crystal. The pyroelectric detector produces an output voltage that is proportional to the infrared radiation that passes through the detector's lens and filter, e.g. the infrared radiation within the predefined wavelength range. The detector produces an alarm based on a predetermined voltage or current threshold. For example, one such threshold in the prior art is where the voltage output from the pyroelectric cell or an associated preamplifier is greater than or equal to 3.25 volts. When such a voltage threshold is exceeded, an alarm signal is generated.
In such systems, the detector is limited to identifying the intensity or power of the infrared radiation within the predefined wavelength range. The filter filters out infrared radiation not within the wavelength range of the filter so that the detection device is only provided a limited spectrum of infrared radiation as is necessary to determine the power of the infrared radiation within the wavelength range. While such a design provides an indication of a hot wheel or hot bearing that results in a voltage or current that exceeds the predetermined threshold voltage or current level, the prior art systems have several limitations in the application to railway systems that detect the heat of a traversing railway vehicle's wheel or bearing. The detection device is dependent on the detection of the power of the filtered infrared radiation as represented by the intensity of the received radiation. Therefore, in situations where this wavelength range is attenuated and/or filtered by external sources, the intensity of infrared radiation within the filtered bandwidth will be reduced. This results in an inaccurate detection of the hot wheel or bearing condition. For example, blowing snow, wind or rain or other weather conditions that exists between the detector and the railway vehicle can attenuate and thereby reduce the amount or intensity of the infrared radiation collected by the detector, thereby reducing the magnitude of infrared radiation within the wavelength range as detected by the detection device. In these cases, the sensed magnitude of radiation is less than the magnitude of radiation that is generated by the wheel or bearing and therefore a hot wheel or hot bearing may go undetected. When this occurs, there is potential for disaster as the undetected hot wheel or hot bearing may fail causing a potentially dangerous situation including a train derailment.
Another such external source which negatively impacts the operation of prior art detection systems is the sun. A “sun shot” occurs when a railway vehicle or car is open thereby allowing direct sunlight to be exposed to the detector. The sun is viewed in the detector's zone of detection and the collected infrared includes the direct sun light. In this situation, the filtered infrared radiation saturates the infrared detection device with considerable infrared radiation from the sun causing the detector to detect higher levels of heat thereby resulting in a false hot wheel or bearing alarm. In a similar situation, the required close proximity of the heat detection device to a high G-force environment (i.e., an environment with high mass times acceleration), which is common with railway systems, has been known to cause a piezoelectric effect in pyroelectric heat detection devices. The piezoelectric effect causes the device to produce a false heat signal or increased level of voltage output. In these cases, the false hot wheel or bearing alarm may result in an unnecessary and unscheduled stop of the train to investigate and perform maintenance. False stops are both time-consuming and costly as they may also cause substantial disruption in train schedules.
As such, there is a need for a hot wheel or hot bearing heat detection system that can accurately detect a temperature range or a temperature of the detected wheel or bearing in the harsh environment of the railway system. Such an improved system will not be susceptible to high G-forces associated with a traversing railway vehicle. An improved system will also accurately detect a temperature range or a temperature of the wheel or bearing when external factors such as snow or rain block a portion of the infrared radiation radiated by the wheel or bearing. Furthermore, an improved system will not be susceptible to inaccurate temperature measurements when the detector is exposed to high levels of direct sunlight.